Scheme of operation of the forced crankcase ventilation system (engine 2.7 l).
System check
1. Disconnect the vent hose from the positive crankcase ventilation valve. Remove the valve from the cylinder head cover and connect it to the ventilation hose.
Engines 2.0 l / 2.4 l. | Engine 2.7 l. |
2. Start the engine and let it idle. Close the valve opening with your finger and check that you can feel the presence of vacuum from the intake manifold.
Note: At this point, the positive crankcase breather valve plunger will move back and forth.
3. If vacuum is not felt, clean the PCV valve and vent hose in a cleaning solution (solvent) or replace if necessary.
Checking the positive crankcase ventilation valve
1. Remove the positive crankcase ventilation valve.
2. Insert a thin rod into the PCV valve from the threaded side and move the rod back and forth to check that the plunger moves.
3. If the plunger does not move, there is a deposit in the PCV valve. In this case, it is necessary to clean or replace the valve.
4. Reinstall the positive crankcase ventilation valve and tighten to rated torque.
- Tightening torque: 8-12 Nm
Description of the operation of the positive crankcase ventilation valve
The forced crankcase ventilation valve is designed to control the flow of crankcase gases bypassed to the intake. The following four modes of operation of the positive crankcase ventilation valve are possible.
A - from the intake manifold; B - from the side of the cylinder head cover; 1 - no vacuum; 2 - average rarefaction; 3 - large vacuum; 4 - low vacuum.
1. There is no vacuum.
When the engine is not running, the valve is completely closed under the action of the main spring and gases from the crankcase do not enter the intake manifold. The valve works similarly with backflash (so-called "shot in the intake"), so that the flame does not enter the crankcase where it can ignite concentrated fuel vapors.
2. Medium rarefaction.
When driving a car with a small load on the engine, the valve spool takes an intermediate position (valve open), allowing a larger amount of crankcase gases to be bypassed.
3. Large vacuum.
When the engine is idling and when the vehicle is slowing down (forced idle) a small amount of crankcase gases is formed, but the vacuum in the intake manifold channel is large. As a result, the valve spool is fully retracted, overcoming the resistance of the springs, and significantly closes the vacuum channel, so that, despite the complete opening of the forced ventilation channel, the bypass of crankcase gases is minimal and excess air is not sucked into the intake from the side of the air filter.
4. Small depression.
When accelerating the car and driving with a heavy load on the engine, a large amount of blow-by gases are formed, so that the valve spool takes a position in which the rarefaction channel has a maximum cross section (PCV valve almost closed). If the amount of crankcase gases formed exceeds the capacity of the valve, then part of them is sent through the ventilation hose to the air filter housing and then to the inlet.